U.S. patent number 4,146,112 [Application Number 05/847,067] was granted by the patent office on 1979-03-27 for sound reducing baffle for electrical apparatus.
This patent grant is currently assigned to General Electric Company. Invention is credited to Gerald O. Usry.
United States Patent |
4,146,112 |
Usry |
March 27, 1979 |
Sound reducing baffle for electrical apparatus
Abstract
A sound reducing baffle for air cooled electrical apparatus with
a ventilated enclosure comprised of a box-like closure member
positioned in front of the ventilating openings and open at the
back and top thereof to permit the transfer of air. The sound is
attenuated by reflections and absorption within the baffle with
little or no interference with the transfer of cooling air to and
from the enclosure.
Inventors: |
Usry; Gerald O. (Rome, GA) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
25299664 |
Appl.
No.: |
05/847,067 |
Filed: |
October 31, 1977 |
Current U.S.
Class: |
181/202; 181/256;
181/264; 181/281; 336/100; 336/59 |
Current CPC
Class: |
H01F
27/33 (20130101); H01F 27/02 (20130101) |
Current International
Class: |
H01F
27/02 (20060101); H01F 27/33 (20060101); H02K
005/24 (); H02K 005/24 () |
Field of
Search: |
;181/204,224,200,201,202,203,205,230,242 ;336/59,100 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hix; L. T.
Assistant Examiner: Fuller; Benjamin R.
Attorney, Agent or Firm: Doyle; Francis X. Menelly; Richard
A.
Claims
I claim:
1. A sound reducing enclosure for convection cooled transformers
comprising:
A transformer housing closed at the top, bottom and sides and
containing a plurality of ventilating openings at the top and
bottom for the passage of air;
A pair of top and bottom baffles each having a pair of opposing
side members, a front member extending between the side members and
a bottom member coextensive with the side members to form an
L-shaped structure said top baffle being mounted at a top exterior
portion of the housing coextensive with the top ventilating
openings and positioned vertically upward external to the housing
for exiting ventilating air from the housing, said bottom baffle
being mounted at a bottom exterior portion of the housing
coextensive with the bottom ventilating openings and with the front
member positioned vertically downward for receiving ventilating air
to the housing.
2. The enclosure of claim 1 further including at least one spacing
member extending between the front member and the housing for
maintaining a predetermined distance between the side members and
the housing.
3. The enclosure of claim 1 further including a layer of sound
absorbing material on the inner surface of the structure for
promoting the attenuation of sound within the structure.
4. A sound reducing enclosure for convection cooled transformers
comprising:
A transformer housing closed at the top, bottom and sides and
containing a plurality of ventilating openings at the top and
bottom for the passage of air:
A pair of top and bottom baffles each having a pair of opposing
side members, a front member extending between the side members and
a bottom member coextensive with the side members to form an
L-shaped structure said top baffle being mounted at a top interior
portion of the housing coextensive with the top ventilating
openings and with the front member positioned vertically downward
internal to the housing for exiting ventilating air from the
housing, said bottom baffle being mounted at a bottom interior
portion of the housing coextensive with the bottom ventilating
openings and with the front member positioned vertically upward for
receiving ventilating air to the housing.
Description
BACKGROUND OF THE INVENTION
This invention relates to sound reducing baffles for use with
air-cooled induction apparatus such as an electrical transformer.
The use of power transformers operating in the kilovolt range
inside residential and commercial buildings may present a noise
problem.
In ventilated dry type transformers, the transformer assembly is
cooled by natural convection currents or by forced air cooling.
Ventilating openings are provided near the top and bottom of the
enclosures in order to permit the free passage of air to the
transformer during the cooling process. In order to reduce the
amount of noise radiated from the transformer enclosure, the inner
walls of the enclosure are frequently lined with a sound absorbing
material. Since the housing is essentially sealed except for the
ventilating openings, and since it has been heretofore impossible
to baffle the sound emanating through the ventilating openings
without interfering with the flow of air necessary to cool the
transformer, they are the main sound transmission path.
One method for attempting to reduce the sound generated within an
air ventilated dry type transformer is described in U.S. Pat. No.
3,451,503. This method provides a Helmholtz resonator mounted
within the transformer enclosure proximate each of the ventilating
openings. The sound, in passing through the ventilating openings,
becomes attenuated to some degree since the resonator cavities are
tuned to the frequency of the generated sound. Each of the
Helmholtz resonators is mounted adjacent each ventilating opening
and particular care is taken not to restrict the ventilating
opening.
The increasing use of power transformers in residential localities
anticipates a further reduction in the amount of noise emanating
from the transformer enclosure. The transformers can generate sound
in excess of 60 dBA and it has been determined that sound levels in
excess of 45 dBA can be uncomfortable, especially in the evening.
The purpose of this invention therefore is to provide sound
attenuating apparatus for use with dry type, air cooled electrical
apparatus to effectively reduce the level of the transformer
generated sound with little or no interference with the transformer
cooling process.
SUMMARY OF THE INVENTION
The invention comprises a sound reducing baffle for air cooled
electrical apparatus and consists of a baffle mounted either
internal, external, or both internally and externally to the
electrical apparatus enclosure. The baffles are specifically
designed to attenuate sound by the mechanism of intensity loss by
reflection by providing a sound barrier in the path of the incoming
and outgoing air flow with little or no interference with the rate
of flow.
One embodiment comprises an L-shaped extended member attached to
the apparatus enclosure and extending outwardly in the vicinity of
the ventilating opening. The large leg of the L faces downward for
the bottom ventilating openings and the large leg of the L is
mounted upwardly for the upper ventilating openings to promote the
flow of air from the bottom to the top of the electrical apparatus
enclosure.
A further embodiment of the sound reducing baffle of this invention
includes a layer of sound absorbing material on the surface of the
baffle facing the enclosure in order to absorb the sound upon
reflection.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side perspective view of a transformer enclosure
assembly for use with the sound reducing baffle of this
invention;
FIG. 2 is a side sectional view of the assembly of FIG. 1 including
air flow directional arrows;
FIG. 3 is a side perspective view of the apparatus of FIG. 1 with a
pair of sound baffles attached according to the invention;
FIGS. 3A to 3E are side sectional views of different embodiments of
the sound reducing baffle of this invention;
FIG. 4 is a side sectional view of the apparatus of FIG. 3
including air flow directional arrows;
FIG. 5 is a top perspective view of the sound reducing baffle of
the invention;
FIG. 6 is a side sectional view of the enclosure of FIG. 3 with the
inventive sound reducing baffles mounted on the interior of the
enclosure;
FIG. 7 is a side sectional view of the enclosure of FIG. 3 with
inventive sound reducing baffles mounted interior and exterior to
the enclosure; and
FIG. 8 is a graphic representation of the sound level reduction as
a function of electrical excitation voltage for the sound reducing
baffle of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The sound reducing baffle of this invention is described for use
with air cooled electrical apparatus of the type shown in FIG. 1. A
metallic housing 10 encloses a transformer 12 of the type having a
yoke 13 attached to a rigid base 14 by means of vibration damping
pads 15. A plurality of structural cross members 16 are usually
employed to provide further support to the housing 10. A plurality
of ventilating openings 11 are provided at the top and bottom of
the housing 10 to promote the free flow of air to within the
interior of the housing 10. In order to attenuate the sound
emanating from the transformer 12, insulation material 17 usually
of a glass fiber type is sometimes applied to the interior surface
of the housing 10. Sound waves generated by the transformer 12 upon
reaching the insulation material 17 lose intensity by means of
absorption within the insulation material 17 and upon reflection
from the surface. Since the top, bottom and sides of the housing 10
are sealed, the principle egress for the sound generated by
transformer 12 is by means of ventilation openings 11.
The ventilating means for cooling the transformer 12 of FIG. 2 is
shown in FIG. 3. The convection air currents indicated by the
directional arrows move from the bottom ventilation opening
hereinafter designated as 11B to the top ventilation opening
hereinafter designated as 11A. The density of the ambient air at
the bottom of the housing 10 is generally greater than the density
of the ambient air near the top of the exterior of the housing 10
and enters into the bottom ventilator opening 11B, contacts the
bottom section 12 and becomes heated upon contact therewith and
decreases in density rapidly rising to the top of the housing 10
until being forced out through top ventilator opening 11A. Since
the sound generated by the transformer 12 exits readily through
each of the ventilation openings 11A, 11B, as indicated by the
radially emanating waves S this invention proposes to substantially
decrease the emanated sound waves S with little or no interference
with the rate of heat transfer away from the transformer 12 as
indicated by the air passage through openings 11a, 11b.
FIG. 3 shows a housing 10 including a transformer 12. The top
mounted baffle 18a of this invention is shown mounted at top of the
housing 10 proximate the top ventilating opening 11a. The top
baffle 18a is fastened to the housing by means of a fastening
member 24 fixedly attached to the baffle 18a for removably mounting
on housing 10. The baffle 18a can be fixedly attached to the
housing 10 by means of welding, but it is preferred to mount the
baffle 18a by some removable means such as for example self tapping
screws. This allows ready access to the plurality of top openings
11a for cleaning and repair. The baffles 18a, 18b, can also be
integrally formed in whole or in part from the material of the
housing 10. The front section 19 (FIG. 5) of the top baffle 18a is
spaced a fixed distance from the housing by means of a plurality of
baffle spacers 23. The top baffle 18a is mounted relative to the
housing 10 such that the top baffle opening described as 22a is
approximately equal to the total cross sectional area defined by
each of the openings 11a. This is necessary to promote good sound
baffling properties with little or no interference with the
transmission of air through the openings 11a. The top baffle 18a is
closed by a side member 21 at both sides thereof and by a bottom
member 20 so that the only means for egress through the opening 11a
is by means of top baffle opening 22a. A bottom baffle member 18b
is mounted at the bottom of the housing 10 (FIG. 4) similar to that
described earlier for top baffle 18a except that the bottom baffle
opening 22b faces downward. The upward direction of top baffle
opening 22a and the downward pointing direction of bottom baffle
opening 22b is to ensure the flow of air from the bottom of housing
10 through bottom baffle 18b to within the housing 10 and out
through the top baffle 18a in the manner as described earlier for
the embodiment of FIG. 2. Both top and bottom baffles 18a, 18b, are
made of sheet metal or plastic and can be formed from a single
piece for convenience in construction. Various configurations for
both top and bottom baffles 18a, 18b are shown in FIGS. 3A to 3E.
The baffles within the embodiments of FIGS. 3A to 3E will be
hereafter described by reference number 18 since the embodiments
are equally applicable to top and bottom mounted devices. The
embodiment of FIG. 3A is mounted with the front 19 forward of the
ventilation opening 11 and includes a layer of insulation material
17 to promote the absorption of sound. The sound directional arrows
S show that the sound is reflected and partially absorbed upon the
surface of the sound absorbing 17 as described earlier for the
embodiments of FIGS. 1 and 2. The embodiment of FIG. 3A therefore
provides for the effective total coverage of the interior of the
housing 10 with sound absorbing material 17.
FIG. 3B is similar to the embodiment of FIG. 3A and includes an
interiorly mounted front section 19. The interior mounted front
section 19 also has a layer of sound absorbing material 17 to
further promote the attenuation of sound originating interior to
the housing 10. The baffle openings 22 for all the embodiments of
this invention are calculated to be equal to or greater in total
surface area than the combined available cross sectional area of
all the ventilating openings 11 in order to ensure that the
transfer of air through the ventilating openings 11 is not
hindered.
FIG. 3C shows an embodiment 18 for greater attenuation for natural
and forced ventilation where a fan is mounted within housing 10 to
promote the transfer of air through the openings 11, the deflector
9 can be employed without seriously interfering with the forced air
flow properties. The deflector 9 can include sound absorbing
material 17 and be mounted to the housing 10 in a manner described
earlier for the embodiments of FIGS. 3A and 3B. The purpose of the
deflector 9 is to force the sound wave S into a plurality of
multiple internal reflections as indicated, thus reducing the
emanating sound level.
FIG. 3D is a further embodiment of the device of FIG. 3C. The
baffle 18 is mounted to the housing 10 relative to the ventilating
opening 11 in a manner similar to that described earlier for FIG.
3C and V-shaped deflector 9 is incorporated within the baffle 18 in
order to provide a plurality of reflecting surfaces for the sound
wave S. It should be noted that the decrease in sound level depends
on the number of reflections that the sound wave S makes before
leaving the housing 10. It should be further noted that the
presence of a sound absorbing material 17 greatly increases the
loss in sound upon reflection since part of the sound is absorbed.
The invention further provides a tortuous path for the sound waves
originating within the housing 10 such that the sound wave must
necessarily contact and become reflected off the interior surface
of the baffle 18 before leaving the housing 10.
FIG. 3E provides a pair of deflectors 9a, 9b for further providing
a tortuous path to sound emanating from opening 11. The deflectors
9a, 9b are mounted external to the housing 10 within baffle 18.
The air flow characteristics for the top and bottom mounted baffles
18a and 18b, of FIG. 3 is shown in detail in FIG. 4. Two top
baffles 18a and two bottom baffles 18b are mounted on the housing
10 but only one of each top and bottom baffle will be described. It
is to be noted that a single top mounted baffle 18a extends along
the surface of the housing 10 to encompass a plurality of
ventilating opening 11a and a single bottom baffle 18b extends
along and operatively encompasses a plurality of bottom ventilating
opening 11b providing that the top and bottom baffle openings 22a,
22b exceed or equal the total cross sectional area provided by the
plurality of top and bottom ventilating openings 11a, 11b. The
circulating air is indicated by arrows in a manner similar to that
described earlier for the housing 10 of FIG. 2 wherein the denser
ambient air enters the bottom baffle 18b by means of the bottom
baffle opening 22b and is carried by convection up through and
across the surface of transformer 12 wherein the air continuously
becomes less dense upon heating, and is forced by incoming air out
through the top baffle 18a through the top baffle opening 22a. As
shown in FIG. 4 sound emanating from within housing 10 will reflect
off the insulating material 17 shown by the individual wave S and
will be substantially decreased in magnitude as well as being
redirected out through the top baffle opening 22a in the direction
indicated by the wave train S. The downwardly directed bottom
baffle opening 22b promotes air flow in the pattern indicated and
the upwardly directed top baffle opening 22a promotes the transfer
of air in the direction of natural convection currents for the
reasons described earlier.
An enlarged view of the top baffle 18a of FIG. 4 is shown in FIG.
5. For a transformer having three top and bottom ventilation
openings on both sides of the transformer housing the ventilation
opening dimensions are approximately 10 .times. 18 inches for each
opening. The front 19 of the baffle 18a measures approximately 11",
and the side 21 and bottom 20 extend approximately 3". The
thickness 25 can be roughly 1/2" depending upon the total length of
the baffle 18. For the embodiment of FIG. 5 the length l is
approximately 6 ft. and the spacers 23 are each approximately 3"
long. The thickness of the insulation material 17 varies depending
upon the composition of material used and the overall intensity of
sound generated by the transformer. The fastener 24 can consist of
a flat plate 7 having a plurality of holes 26 for bolting the
baffle 18a to the transformer housing 10. A screen material is
generally provided over the ventilation openings 11 or a plurality
of perforations are embossed into the housing 10 having the
dimensions as described earlier. For the baffle 18a of the
invention, the embossed perforations and/or the screen material can
be omitted, and the ventilating openings 11 can be cut directly
from the housing 10 in order to provide better air transmission and
a screen 27 can be provided to the baffle opening 22a to perform
the same function and purpose of the screen and/or perforations as
applied to the housing 10. The baffle 18a as shown in FIG. 5 can be
applied to an already installed housing 10 as described generally
in FIG. 1 in response to a customer's complaint that the existing
noise levels emanating from the housing 10 are uncomfortable. A
plurality of baffles 18a can be installed in the field by simply
drilling into the housing structure and fastening the baffle 18a by
means of the holes provided as indicated at 26. The sound
attenuating baffles of this invention can also be welded in the
field or during the fabrication of the housing as described
earlier.
FIG. 6 shows an embodiment of the sound attenuating baffle 18 of
this invention mounted on the interior surface of housing 10. In
this embodiment the top baffle 18a is mounted with top baffle
opening 22a facing downward and with insulation layer 17 interior
to the housing 10. The bottom baffle 18b is mounted with the bottom
baffle opening 22b facing upward which is directly opposite to the
external mounted top and bottom baffles 18a and 18b for the
embodiment of FIG. 2. This embodiment provides for nearly complete
coverage of the interior of the housing 10 with insulating material
17 and is a very effective method for mounting the sound
attenuating baffles 18 of this invention during the transformer
manufacturing process. The internally mounted top and bottom
baffles 18a, 18b can be mounted in the field in the manner
described earlier for the embodiment of FIGS. 4 and 5 but it is
more convenient to mount the baffles 18 when mounting the
transformer 12 within the housing 10.
An extremely efficient application for the sound attenuating
baffles of this invention can be seen by referring to FIG. 7. Here
a pair of top baffle members 18a are mounted at the top of the
housing 10 and a pair of bottom baffles 18b are mounted at the
bottom thereof. As shown by the air direction arrows, the flow of
air into the housing 10 is not seriously interfered with whereas
the transfer of sound is seriously impeded by the tortuous path
presented by the top and bottom baffle pairs 18a, 18b. It is to be
noted that the bottom baffle openings 22b for the pair of internal
and external mounted bottom baffles 18b are equal to or greater
than the cross sectional area of the bottom ventilating openings
11b and the top baffle openings 22a for the pair of top baffles 18a
is greater than or equal to the top ventilating openings 11a for
the reasons described earlier. The presence of the insulation layer
17 on both the internal and external mounted top and bottom baffles
18a, 18b, greatly reduces the amount of sound emanating from the
housing 10 and the sound level can be further decreased if an
additional insulation layer 17 is placed on the outwardly facing
surface 6 of the internally mounted top and bottom baffles 18a,
18b.
The measured sound level reduction values in dBA units for the
transformer 12 shown in all the embodiments of this invention is
shown graphically in FIG. 8. The zero sound reduction level
indicated by the dotted line A is for the embodiment of FIG. 1
which contains a transformer 12 mounted within a standard housing
10 with no baffle means provided. Curve B indicates the sound
reduction for the embodiment of FIG. 3 with top and bottom baffles
18a, 18b with no insulation 17 provided on the baffles. Curve C
indicates the sound level reduction for the same embodiment of FIG.
3 with a layer of sound absorbing material 17 mounted on the inner
surface. The sound reduction values for B and C are plotted as
functions of the excitation voltage applied to the transformer
12.
The sound level reduction measurements for the embodiment of FIGS.
6 and 7 have not as yet been determined but calculations indicate
that sound level reductions as great as 10 dBA can be achieved with
the embodiment of FIG. 7 and slightly less than 10 dBA can be
achieved with the embodiment of FIG. 6.
Although the sound attenuating baffle of this invention is
described for enclosures containing air cooled power transformers,
this is by way of example only. The sound attenuating baffles of
this invention readily provide sound attenuation to any enclosure
containing electrical apparatus requiring ventilation means for
cooling and/or access to the apparatus enclosed.
* * * * *